The present invention relates to a surface coating composition which is capable of forming a coating layer having excellent gas barrier properties, transparency, and flexibility, and resin moldings, wrapping materials, substrates of liquid crystal displays, and liquid crystal display devices including the substrates which have the coating layer.
For wrapping materials, various physical properties are required. For example, the Japan Industrial Standard No. Z 1707 defines the performances and physical properties required for food wrap plastic films by classifying them into grade classes. The required performances and physical properties depend on the food to be wrapped, and examples thereof include: mechanical properties such as tensile strength, elongation, and impact strength; heat-sealing properties; low temperature resistance; heat resistance; resistance to oils and greases. In addition to the above, the gas barrier properties such as moisture permeability (water vapor permeability), oxygen permeability, and carbon dioxide permeability are required in general. The gas barrier properties are important properties not only for food wrap materials but also for various wrapping materials for phamaceuticals, electronic components, and the like.
Known methods for giving gas barrier properties to resin moldings such as plastic films and plastic sheets include: (1) the method of forming a moldings by using a gas-impermeable material such as ethylene-vinyl alcohol copolymer, vinylidene chloride copolymer, aromatic nylon, and the like; (2) the method of laminating or coating such a gas-impermeable material on other materials; (3) the method of laminating an aluminum foil on a film material; and (4) the method of depositing a metal oxide.
However, of the gas-impermeable material used in method (1), ethylene-vinyl alcohol copolymer and aromatic nylon have the problem that the gas-barrier properties significantly deteriorate with moisture adsorption due to its poor moisture resistance. Vinylidene chloride copolymers have chlorine atoms and thus might cause environmental pollution. In method (3), an aluminum foil-laminated film makes a packaged content invisible from the outside. In method (4), a metal-deposited film has the problem that, due to its poor flexibility, cracks easily occur in the deposited layer during packaging. As a result, the gas barrier properties are deteriorated.
Under such circumstances, as to a wrapping material, there has been a demand for developing a surface coating composition which is capable of forming a coating layer exhibiting excellent gas barrier properties, heat resistance, flexibility, transparency, moisture resistance, and resistance to solvent.
In a field of liquid crystal display devices as well, there has been a demand for the surface coating composition capable of forming a coating layer which exhibits excellent gas barrier properties. A liquid crystal display device is used in various applications such as watches, electric calculators, panels for automobiles, pager and the like. FIG. 1 is a diagram schematically showing a simplified structure of a liquid crystal display device. A liquid crystal display device 1 includes a cell formed by substrates 2, 2, alignment layers 3, 3, and transparent electrodes 4, 4, all of which are opposed to each other. The cell is filled with a liquid crystal composition 5 and is sealed by epoxy resin 6. As used in wider applications, the liquid crystal display device is required to have thin thickness and light weight at low production cost. To satisfy such demands, recently, the substrates 2 are made of plastic film instead of glass in many cases. The substrates are required to be excellent in physical properties such as heat resistance, flexibility, transparency, moisture resistance, and resistance to solvent, and the substrate made of plastic film satisfies these requirements. In this case, however, there is a problem as follows. As described above, the liquid crystal composition 5 is sealed inside the cell formed by the substrates 2 opposed to each other under reduced pressure. If the plastic film has high gas permeability, it allows gases such as oxygen and nitrogen to pass therethrough, causing generation of air bubbles inside the cell.
To solve such a problem, it has been suggested to give the gas barrier properties to the plastic film used as a substrate. However, such a substrate is not adequate for a liquid crystal display device, because it has only poor moisture resistance and its gas barrier properties deteriorate in the presence of moisture.
Furthermore, in the recent situation where the liquid crystal display devices are used in wider applications, only the use of plastic film in stead of glass is not sufficient to satisfy the requirements of downsizing and low production cost of liquid crystal display devices. From such viewpoints, studies have been conducted to develop transparent electrodes, which are components indispensable for liquid crystal display devices, having thinner thickness. Currently, the transparent electrodes are mainly made of indium tin oxide (ITO) layer. The ITO layer is formed by providing ITO onto a transparent plastic film by a method such as coating and sputtering. In this case, an undercoat layer is interposed between the ITO layer and the transparent plastic film; otherwise, they do not sufficiently attach to each other. However, the presence of undercoat layer constitutes a restriction in realizing the thin thickness and low production cost of the liquid crystal display devices.
The prevent invention has been conducted to solve the above-described problems, and the objective thereof is to provide a surface coating composition which is capable of forming a coating layer having excellent gas barrier properties, heat resistance, flexibility, transparency, moisture resistance, resistance to solvent and the like.
The another objective thereof is: to provide a wrapping material for food, pharmaceuticals, electronic components; and to provide high-performance substrates for use in a liquid crystal display device. The substrate makes it possible to downsize the liquid crystal display devices.